Computer Crashes After Start Up Then is Fine?

[BriggsJack]

Hello, my computer is crashing in a very strange way and im really not sure what causes it. My computer will crash about 5-10 minutes after startup and then restart, after it restarts it is fine to use for an indefinite period. I have tried reinstall windows and cleaning the heat sink. All of the fans are operating properly and the computer often does not feel hot after the crash, I have run a virus scan and my computer seems clean. What can I do? Any help is appreciated.

 

[iceblitzed]

If you have Windows 8 (not 8.1) windows 7, vista, or xp you can download a malware program called combofix.exe
http://www.bleepingcomputer.com/download/combofix/
It usually detects things other programs cannot.